Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $70.92   8.661%   $77.0624   $77.06   $77.05   $77.10  
  Purchase #2 $52.74   4.668%   $55.2019   $55.20   $55.20   $55.20  
  Purchase #3 $97.66   4.519%   $102.0733   $102.07   $102.05   $102.10  
  Purchase #4 $244.30   7.200%   $261.8896   $261.89   $261.90   $261.90  
  Purchase #5 $211.79   5.675%   $223.8091   $223.81   $223.80   $223.80  
  Purchase #6 $139.84   12.381%   $157.1536   $157.15   $157.15   $157.20  
  Purchase #7 $156.87   8.129%   $169.622   $169.62   $169.60   $169.60  
  7 purchase totals = $974.12       $1,046.8119   $1,046.80   $1,046.75   $1,046.90